Ingvild Marstein Olsen (20), began The Topless Tour with her English friends Olivia Edginton (20) and Lydia Buckler (21) last summer, when the trio decided to strip off for a topless snap while trekking around Lake Mjøsa near Lillehammer.
"We started just for fun, quite spontaneously," Marstein Olsen, who studies dance with the other girls in London, told Norway's Dagbladet newspaper.
Since the Mjøsa photos, the trio have added topless pics taken in Oslo, New York, Manchester, Berlin and London.
It's not quite as racy as you might hope, however, as all of the photographs are taken from behind.
"The Topless Tour is the opening of your bare chest and heart to the world," Edginton, 20, told the UK's Daily Mail newspaper. "It sounds really cheesy on paper, but it really connects you with the people you love. The experience is a whirlwind of different emotions and it’s so nice to share it with others."
Since the trio launched the project in early 2013, the trio have gained 8,000 followers on Facebook, and inspired scores of imitators who send in pictures to to be posted to the page.
"Many people have contacted us and written that they think it's fun, and good that they can show who they are, regardless of gender and size of the body," Marstein Olsen said.
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This summer, The Topless Tour plans to visit Italy, Croatia and Sweden.
You can see a selection of pictures from The Topless Tour here.